To paraphrase Lord Kelvin, if you don’t measure you can’t improve. Our data center operations team lives by this credo, and we take every opportunity to measure the performance of our facilities. In the same way that you might examine your electricity bill and then tweak the thermostat, we constantly track our energy consumption and use that data to make improvements to our infrastructure. As a result, our data centers use 50 percent less energy than the typical data center.

One of the measurements we track is PUE, or power usage effectiveness. PUE is a ratio of the total power used to run a data center to the amount used to power the servers. For instance, if a data center has a PUE of 2.0, that means that for every watt of energy that powers the servers, another watt powers the cooling, lighting and other systems. An ideal PUE would be 1.0.

In 2011, our trailing 12-month average PUE was approximately 1.14—an improvement from 1.16 in 2010. In other words, our data centers use only 14 percent additional power for all sources of overhead combined. To calculate this number we include everything that contributes to energy consumption in our data centers. That means that in addition to the electricity used to power the servers and cooling systems, we incorporate the oil and natural gas that heat our offices. We also account for system inefficiencies like transformer, cable and UPS losses and generator parasitic energy draw.

If we chose to use a simpler calculation—for instance, if we included only the data center and the cooling equipment—we could report a PUE as low as 1.06 at our most efficient location. But we want to be as comprehensive as possible in our measurements. You can see the difference in this graphic:

We’ve been publishing our PUE quarterly since 2008—in fact, we were the first company to do so, and are still the only one. Our numbers are based on actual production data taken from hundreds of meters installed throughout our data centers, not design specs or best-case scenarios. One way to think of it is comparing a car manufacturer’s mileage estimates for a new model car to the car’s real-life miles per gallon. We’re measuring real-world mileage so we can improve real-world efficiency.

Our 2011 numbers and more are available for closer examination on our data center site. We’ve learned a lot through building and operating our data centers, so we’ve also shared our best practices. These include steps like raising the temperature on the server floor and using the natural environment to cool the data center, whether it’s outside air or recycled water.

We’ve seen dramatic improvements in efficiency throughout the industry in recent years, but there’s still a lot we can do. Sharing comprehensive measurement data and ideas for improvement can help us all move forward.